The present invention relates to a constant-current circuit incorporating an insulated-gate type field-effect transistor (referred to simply as MISFET, hereinafter) and to a signal converter making use of the constant-current circuit.
The drain current of MISFET, e.g. an enhancement-mode MISFET, in the saturated state of the same, is substantially constant even when the drain voltage is varied. This characteristic can conveniently be used for realizing a constant-current circuit. The drain current of the enhancement-mode MISFET, however, exhibits a tendency to increase as the drain voltage is increased, due to the channel length modulation. Thus, the constant-current circuit incorporating the enhancement-mode MISFET does not always exhibit a good constant-current characteristic.